In optical communication systems, a transceiver generally includes a transmitter optical subassembly (TOSA) and a receiver optical subassembly (ROSA). The TOSA encloses a light-emitting device, typically a laser diode (LD), to emit light as signals, while the ROSA installs a light-receiving device, typically a photodiode (PD), to receive the light signals. To achieve a precise signal, it is needed to test the transceiver's performance after they have been manufactured.